In general, a plasma processing apparatus for performing a plasma processing on a circular plate shaped wafer includes a processing chamber for accommodating therein the wafer, a shower head for supplying a processing gas into the processing chamber and a mounting table for mounting thereon the wafer. The mounting table is connected to a high frequency power supply and serves as an electrode for applying a high frequency power into the processing chamber. Such a plasma processing apparatus performs a plasma processing on the wafer by using ions and/or radicals generated by converting the processing gas supplied to the processing chamber into a plasma with the high frequency power applied thereto.
Further, the plasma processing apparatus has a ring-shaped focus ring installed to surround an outer periphery of the wafer mounted on the mounting table in the processing chamber. The focus ring has a double ring structure, including a ring-shaped inner focus ring member provided at an inner portion and a ring-shaped outer focus ring member provided to surround an outer periphery of the inner focus ring member. The inner focus ring member is made of a conductive material such as silicon or the like, whereas the outer focus ring member is made of an insulating material such as quartz or the like. The inner focus ring member concentrates or collects the plasma on the wafer, and the outer focus ring member serves as an insulator for confining the plasma on the wafer.
During the plasma processing, the temperature of the outer focus ring member increases due to a heat from the plasma. However, if the temperature thereof is unstably maintained, an ion and/or a radical density near the outer focus ring member becomes non-uniform, causing the ion and/or radical density in an outer peripheral portion of the wafer to also become non-uniform. Consequently, the central and the peripheral portion of the wafer are plasma-processed differently, which makes it difficult to carry out a uniform plasma processing on the wafer. In addition, as a consequence of the outer focus ring member being scaled up to meet a recent trend for the larger diameter wafer, the temperature rising rate of the outer focus ring member decreases, requiring more time for the temperature to reach a specific value and remain stable thereat. As a result, it becomes difficult to perform a uniform plasma processing on the wafer, which in turn deteriorates a production yield.
To this end, recently, there is developed an outer focus ring member having therein a heater (see, e.g., Japanese Patent Laid-open Application No. 2000-36490 (hereinafter, referred to as “Patent Document”). In such an outer focus ring member, the temperature thereof can be stably maintained rather rapidly by controlling the heater, allowing a uniform plasma processing to be performed on the wafer.
In a plasma processing apparatus, dummy wafer are generally processed first with a recipe identical to that to be used in an actual production lot processing in order to stabilize an inner atmosphere of a processing chamber prior to starting the production lot processing. However, during the processing of the dummy wafers, deposits, i.e., reaction products of the processing gas, get deposited on the surface of the outer focus ring member if the temperature thereof has not increased enough. As the production lot processing continues, the deposits gradually get peeled off and then get adhered to the wafer as particles, which in turn detrimentally affects the production yield of the wafer. Accordingly, there arises a need to shorten a cleaning process cycle for removing the deposits from the outer focus ring member.
In the technical field of a CVD(chemical vapor deposition) plasma processing apparatus, it is well known that deposits can be removed fast by increasing the temperature of the member to which the deposits are adhered and the member can also be maintained in a condition where deposits can hardly be produced by maintaining the member at a high temperature. In case of using outer focus ring member of the aforementioned Patent Document, the deposits can be removed from the outer focus ring member by increasing the temperature of the outer focus ring member by controlling the heater. And then, the member can also be maintained in a condition where deposits can hardly be produced, which can prevent particles from adhering to the wafer and, also, a cleaning cycle can be lengthened.
The outer focus ring member is consumed by ions or the like colliding therewith during the plasma processing, requiring it to be regularly replaced. Since, however, the manufacturing cost as well as the running cost of using the outer focus ring member of the Patent Document is high because of the heater embedded therein. Further, a required wiring process of the heater complicates the replacement of the member and deteriorates the maintenability. It is also necessary to provide wiring for the heater in the mounting table. For such reasons, the outer focus ring member of the Patent Document may not be readily adopted.